1. Field of the Invention
The present invention relates to extension ladders. More specifically, it relates to a replacement rung for an extension ladder. Even more specifically, it relates to a replacement rung that serves to replace the existing pulley on an extension ladder by providing an internally mounted rod within the rung. The rod is mounted on bearings that allow it to spin freely about its long axis. Additionally, the present invention includes a notch or cutout in the replacement rung to allow the rope to be passed over the rotatable rod. More generally, the present invention would serve in any application wherein the rope may inadvertently be dislodged or become jammed against the pulley and a replacement for the pulley is desired.
Thus it can be seen that the potential fields of use for this invention are myriad and the particular preferred embodiment described herein is in no way meant to limit the use of the invention to the particular field chosen for exposition of the details of the invention.
A comprehensive listing of all the possible fields to which this invention may be applied is limited only by the imagination and is therefore not provided herein. Some of the more obvious applications are mentioned herein in the interest of providing a full and complete disclosure of the unique properties of this previously unknown general purpose article of manufacture. It is to be understood from the outset that the scope of this invention is not limited to these fields or to the specific examples of potential uses presented hereinafter.
2. Description of the Prior Art
Extension ladders are well known devices and have been used for many years to allow for efficient storage and portability. In the most common of these types of ladders, the extension is accomplished by fixing one end of a cord to a rung proximate the bottom of the ladder section that will move in relation to the other and run the cord through a pulley proximate the top of the fixed ladder segment. Thus, the user can pull the cord to propel the movable ladder segment upwards. One of the disadvantages of this type of arrangement is that the cord or rope can slip off of the pulley and become jammed. This likelihood increases if the force is applied sideways. The present invention addresses this problem by providing a rotating rod within the ladder rung that extends substantially from one side of the ladder to the other. Thus, the rope is free to slide from side to side while the user is pulling on it to extend the movable ladder portion. A number of patents have been issued that relate to this invention and they are discussed hereinafter:
First is U.S. Pat. No. 190,085 issued to Obadiah Sherwood, Jr. on Apr. 24, 1877. This discloses a fire escape wherein a pair of ropes and a pair of pulleys are used to extend the ladder segments. This is dissimilar from the present invention in that a grooved pulley is specified and no teaching of a smooth rotating rod extending substantially from one side of the ladder to the other is disclosed.
U.S. Pat. No. 333,784 issued to John Royds on Jan. 5, 1886 discloses an extension ladder. Unlike the present invention, there is no teaching of the smooth bar rotatable within a ladder rung and extending across the width of the ladder to serve as a pulley. The pulleys seen in the Royds disclosure are decidedly concave in their rope receiving areas.
Next is U.S. Pat. No. 843,989 issued to Martin Bauer on Feb. 12, 1907. This discloses a combined ladder and scaffold. An extending portion of the ladder is shown, however, no rope or pulley means for the extension thereof is disclosed.
In U.S. Pat. No. 1,912,331 issued to Anders Wikstrand on May 30, 1933 there is disclosed a ladder like structure wherein overlapping sections and locking means between the same are provided for ease of transportation. This invention shows the rope passed over one of the ladder rungs, however the specification states that the rungs are so fastened to the walls of the ladder that the turning of the rungs is prevented. This, in addition to the fact that no rope carrying member is taught being disposed within the rung itself with a cutout for access thereto, make Wikstrand clearly dissimilar from the present invention.
U.S. Pat. No. 3,347,340 issued to Harold W. Huska on Oct. 17, 1967 discloses an extension ladder where the fly section is hoisted over the base by an endless cable or rope moving about the outside of, and through two rungs of the base section, and where a depending loop is attached to a bracket on the outside of the fly section. This is clearly unlike the present invention in that no pulley type of structure is shown.
Lastly, U.S. Pat. No. 4,232,761 issued to Reginald C. Philips on Nov. 11, 1980 discloses an extensible ladder. In this device, the rope is wound on a pivotable rung, however in contrast to the present invention, there is no teaching of an internally located rotatable rod for serving as a pulley in the device.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.